The present invention relates to an electromagnetic shutter in a camera having an exposure control circuit, and, more particularly, to an electromagnetic shutter of the type described above which generates a shutter blade closure detecting signal for enabling the shutter to be used in a fully automated camera sequential operation control circuit without causing any false functions.
A prior art electromagnetic shutter has a rotatable sector ring for permitting the shutter blades to be swung between the fully closed positions and the fully opened positions, shutter blade closing spring means for driving the sector ring so as to swing the shutter blades to the fully closed positions, and electromagnetic driving means including a rotor made of a permanent magnet and a stationary electric coil cooperating with the rotor, which rotor is coupled with the sector ring. When the electric coil is energized and continues to be energized by an exposure control circuit, the sector ring is driven by the rotor so as to open the shutter blades from the closed position and continue to open against the action of the shutter blade closing spring means during the time the electric coil continues to be energized. After a predetermined time period for the proper exposure, when the electric coil is deenergized by the operation of the exposure control circuit, the sector ring is driven by the shutter blade closing spring means so as to close the shutter blades to terminate the proper exposure.
It has also been proposed to use electromagnetic driving means including a stationary permanent magnet and a movable electric coil cooperating with the stationary permanent magnet in place of the above described electromagnetic driving means. Such an electromagnetic shutter is disclosed in Japanese Patent Public Disclosure No. 101924/80.
Since the prior art electromagnetic shutters, however, utilize the shutter blade closing spring means, the shutter blades must be opened and kept opened for the proper exposure against the action of the shutter blade closing spring means by the electromagnetic driving means which must be energized and kept energized during the proper exposure time period, and, therefore, the consumed electric current is very large. Further, since the opening operation of the shutter blades is effected by the differential force between the electromagnetic driving means and the shutter blade closing spring means, the opening operation of the shutter blades is unstable and suffers from a large fluctuation of the operation of the shutter blades.
This is particularly remarkable in the case of an electromagnetic programming shutter in which the shutter blades serve as a diaphragm stop, i.e. the shutter blades are closed before they are fully opened depending upon the scene brightness, so that the opening velocity of the shutter blades varies widely and the operation of the shutter is made very unstable.
Further, when an electromagnetic shutter is used with an automatic camera sequential operation control circuit so as to effect automatically and sequentially the lens focusing, lens resetting, film winding and film rewinding, etc., means is required in order to accurately effect the above described sequential operations without fail, which generates a shutter blade closure detecting signal when the shutter blades are brought to the closed position and supplies the signal to the sequential operation control circuit.
Heretofore, a contact switch has been used for generating the shutter blade closure detecting signal which is actuated by the movement of the sector ring. However, loss of mechanical energy due to the movement of the mechanical parts of the contact switch and loss of electric energy due to the connection and disconnection of the contacts of the contact switch can not be avoided.